var code ; //在全局 定义验证码
function createCode(){
  code = new Array();
  var codeLength = 4;//验证码的长度
  var checkCode = document.getElementById("checkCode");
  checkCode.value = "";

  var selectChar = new Array(2,3,4,5,6,7,8,9,'A','B','C','D','E','F','G','H','J','K','L','M','N','P','Q','R','S','T','U','V','W','X','Y','Z');

  for(var i=0;i<codeLength;i++) {
    var charIndex = Math.floor(Math.random()*32);
    code +=selectChar[charIndex];
  }
  if(code.length != codeLength){
    createCode();
  }
  checkCode.value = code;
}

function validate () {
  var inputCode = document.getElementById("input1").value.toUpperCase();

  if(inputCode.length <=0) {
    alert("请输入验证码！");
    return false;
  }
  else if(inputCode != code ){
    alert("验证码输入错误！");
    createCode();
    return false;
  }
  else {
    alert("成功！");
    return true;
  }
}
